A molten metal, such as aluminum or an aluminum alloy, can be poured into a mold from a tundish. The tundish is a refractory vessel with one or more refractory nozzles located at its bottom or base. A ladle is typically used to transport the molten metal into the tundish from a melting or holding furnace. The molten metal in the tundish flows through the opening in the nozzle and into the sprue of a mold placed underneath it. The sprue originates on the exterior of the mold typically as a cup, or pouring basin, and defines the downward channel through which molten metal enters the mold cavity. The term sprue is generally used herein to describe the sprue cup or other structure into which molten metal is poured into the mold. The objective is to have the molten metal enter the mold cavity with a minimum of turbulence, exposure to air, and temperature loss, which will minimize oxidation and the formation of dross.
Typically, the nozzle of the tundish is a distance from the sprue when molten metal is poured. Consequently, the flow of metal from the nozzle to the sprue is relatively uncontrolled and occurs in air. The turbulence in air accelerates oxidation, which degrades thc pouring process. Uncontrolled flow in air can lead to undesired splashing of the molten metal. As the mold is topped off, it is difficult to control the presence of excess molten metal in the top of the sprue. Bringing the nozzle in close contact with the sprue eliminates some of these problems. However, this alone will neither ensure a laminar flow through the opening in the nozzle and into the sprue nor prevent the presence of excess molten metal in the sprue.
The present invention provides for the pouring of molten metal from a vessel while the vessel's pouring nozzle is in close contact with the mold, and associated components, particularly the stopper rod, extend into the mold sprue. Since the opening in the nozzle is at a minimum height above the sprue, flow of the metal through the opening is at a relatively low velocity. This flow condition will minimize downsprue turbulence. Flow of the molten metal through the opening in the nozzle is controlled with a stopper that produces a smooth laminar flow through the opening when the stopper is in the opened position. In the closed position, the stopper prevents flow through the opening in the nozzle. More important, since the stopper protrudes through the opening in the nozzle and partially into the sprue when the stopper rod is in the closed position, excess molten metal is eliminated in the sprue at the end of the mold filling process. By eliminating this excess, a cumulative savings in molten metal can be realized.